There are presently available various kinds of packaging for sterile specimens. The sterile specimens may be biological, marine, or agricultural specimens stored for analysis in a laboratory. The sterile specimen may also be human or animal tissue for use in transplants.
Human tissue transplant operations have become commonplace in recent times. The success of these transplant operations has created a high demand for the human tissue. However, it is often difficult to find fresh donor tissue for immediate transplant to a recipient. Donor tissue must match the recipient's tissue as closely as possible, to minimize the risk of tissue rejection by the recipient's immune system, and for that reason homografts are preferred; heart valves and blood vessels are two examples of human tissue currently used for human homografts. The tissue is preferably perserved and stored for later implant so that a supply of tissue is on hand independently of immediate donor availability.
Human and animal tissue is preferably cryopreserved for storage beyond a few hours. The tissue, after excision from the donor and suitable treatment as known to those skilled in the art, is stored in a sterile package impermeable to bacteria and then frozen, after which the frozen tissue is stored at a low temperature for relatively long-term preservation. Because the low temperatures required for effective cryopreservation are not attainable by economically-feasible mechanical refrigeration equipment, the packaged tissue specimens are stored by immersion in liquid nitrogen to maintain the cryopreserved tissue viable throughout storage. It is, therefore, important that the storage package be impermeable to liquid nitrogen. When a suitable recipient is found for the tissue, the storage package is removed from the liquid nitrogen storage facility. The tissue is then thawed and removed from its storage package immediately before implant in the recipient.
The tissue must be kept sterile during removal from the storage package before implanting in the recipient. This is not a trivial requirement, as the exterior surface of the storage package is nonsterile or is presumed as such. The sterile packages known in the prior art are inadequate for storing cryopreserved human or animal tissue specimens, because these packages cannot insure the sterility of the specimen when the package is stored in an unsterile coolant medium such as liquid nitrogen. Packaging material impermeable to liquid nitrogen is well known, metallic foil being one example, but simply making the prior art packaging out of material impermeable to liquid nitrogen does not solve the problems of sterility. Because the outer surface of such an envelope is unsterile, there is a risk of contamination of the specimen when the envelope is cut open and the specimen is pulled out of the envelope.
Foil envelopes or pouches with a peel-back opening feature have been proposed as a solution to the foregoing problem. A peel-back opening allows an envelope to be opened by pulling apart the two sides of the envelope, so that the contents are exposed and can be removed without contacting the outer surface of the envelope. However, the outer surface of any single-envelope package is always considered unsterile. A further problem with a single envelope package is that an envelope with a peel-back opening feature is not impermeable to liquid nitrogen. Since a single-envelope package for storing specimens in liquid nitrogen cannot have a peel-back opening, the envelope must be cut open to remove the specimen. There is then a substantial risk that the specimen will make actual physical contact with the unsterile outer surface or opening of the envelope and become contaminated.
Various double-envelope packages for storing sterile specimens have been proposed. A typical double envelope package for storing specimens is also inadequate for insuring sterility of a cryopreserved specimen. A typical double envelope package is made of a sterile inner envelope that contains the specimen, and this inner envelope is stored in an outer envelope impermeable to liquid nitrogen. When the outer envelope is cut open and the inner envelope is removed, there is a substantial risk that the sterile outer surface of the inner envelope will become contaminated from contact with the unsterile outer surface of the outer envelope. Likewise, when the sterile specimen is removed from the inner envelope, there is some risk that the specimen will be contaminated by the presumed-unsterile outer surface of the inner envelope. Making the inner bag with a peel-back opening in a two-envelope package does not solve the problem of sterility. The tissue specimen is stored in a liquid medium in the inner envelope. If the inner envelope is opened by peeling off part of the inner envelope, the liquid will pour uncontrollably out of the inner envelope, and contact the outside surface of the inner envelope, causing inconvenience and a further risk of contamination to the specimen.
Therefore, there is a need for a package for storing sterile tissue specimens in a coolant medium such as liquid nitrogen and maintaining the sterility of the tissue specimen when the specimen is removed from the packaging.